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Abstract

High Altitude Stratospheric Platforms (HASPs) have gained much of attention from the scientific society and the communication industry in the recent years. Their use in the Next Generation Networks can offer enhanced coverage and facilitate the implementation of several heterogeneous wireless networks schemes. In this chapter, the main aspects of the HASP-related technology are presented. Emphasis is given in the ways the intrinsic characteristics of these platforms can be used effectively in order to compensate for the disadvantages of both the existing terrestrial and satellite solutions. Antennas and coverage planning, capacity and interference, call admission control, handover, mobility management, networking and TCP/IP performance are the main issues addressed. The provided mathematical tools and the state-of-the-art techniques presented here, can be useful to engineers interested in designing and evaluating performance of HASP-aided hybrid networks.

Introduction

Ubiquitous coverage and integration of different technologies are key characteristics of the Next Generation Networks. High quality wireless services will aim to subscribers of different types, either fixed or mobile, in remote or highly-density areas, with different propagation characteristics and different bandwidth, delay and jitter demands, depending on the type of service. The terrestrial cellular network is a good candidate as a base for the deployment of a platform offering a greater variety of services than the traditional voice/data/video services currently offered by the 3G cellular systems. Nevertheless, the extended high-cost terrestrial infrastructure in terms of base stations and the multipath phenomena especially in urban areas are issues that cannot be neglected. As for the satellite solutions, they suffer from increased delay, huge cost of development and low capacity. Dealing with the so-called ‘last mile’ problem, i.e. reliable delivery of information between the access point and the end-user, is a matter of concern. High Altitude Stratospheric Platforms (HASPs) seem to be telecommunication components that can alleviate these limitations and be part of effective heterogeneous architectures. HASPs are unmanned airships that fly on the stratosphere at altitudes between 17 and 22 kilometers and offer wireless coverage in areas on the ground.(Djuknic, Friedenfelds & Okunev, 1997) They are equipped with multi-beam smart adaptive antenna arrays that can illuminate certain areas with a variety of ways. They are also known as High Altitude Platforms (HAPs), High Altitude Aeronautical Platforms (HAAPs) and High Altitude Long Endurance (HALE) platforms. In order to achieve easier integration, HASPs can be based on existing communication standards with some modifications suitable for their operational environment. (Grace et al., 2005)

The use of HASPs is characterized by several advantages. HASPs can replace or fill the gaps in existing ground infrastructures, especially in remote areas with deficient or corrupted base stations. Compared with the terrestrial systems, HASPs offer mainly Line-of-Sight (LOS) links, thus they perform better in terms of propagation and rain attenuation, offering large capacity at the same time. The capacity offered from HASPs is significantly larger in comparison with the satellite systems. They also offer better link budget and lower delay than satellites. In addition, developing and putting in service a stratospheric platform is a more cost effective solution than developing a satellite. The reason is that less sophisticated equipment is used and no launch is required. HASPs are environmentally friendly owing to the use of alternative power resources like fuel-cells and solar power. (Tozer, 2000)

HASP Master Control Station (HMCS): A ground station that controls the functionality of a HASP and deals with offered services, network management, dynamic cell planning and power control issues.

TCP Splitting: The practice of using intermediate agents between two end users in order to enhance the TCP performance. A HASP can be the intermediate agent in a hybrid HASP/Satellite network.

Margin Adaption Factor: A factor that is added in the add and drop margins of the handoff procedure in order to dynamically respond to the loading conditions of the base stations and reduce the call dropping probability.